/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package javax.swing.text;

import java.io.*;
import java.text.*;
import java.util.*;
import javax.swing.*;

/**
 * <code>MaskFormatter</code> is used to format and edit strings. The behavior
 * of a <code>MaskFormatter</code> is controlled by way of a String mask
 * that specifies the valid characters that can be contained at a particular
 * location in the <code>Document</code> model. The following characters can
 * be specified:
 *
 * <table border=1 summary="Valid characters and their descriptions">
 * <tr>
 * <th>Character&nbsp;</th>
 * <th><p style="text-align:left">Description</p></th>
 * </tr>
 * <tr>
 * <td>#</td>
 * <td>Any valid number, uses <code>Character.isDigit</code>.</td>
 * </tr>
 * <tr>
 * <td>'</td>
 * <td>Escape character, used to escape any of the
 * special formatting characters.</td>
 * </tr>
 * <tr>
 * <td>U</td><td>Any character (<code>Character.isLetter</code>). All
 * lowercase letters are mapped to upper case.</td>
 * </tr>
 * <tr><td>L</td><td>Any character (<code>Character.isLetter</code>). All
 * upper case letters are mapped to lower case.</td>
 * </tr>
 * <tr><td>A</td><td>Any character or number (<code>Character.isLetter</code>
 * or <code>Character.isDigit</code>)</td>
 * </tr>
 * <tr><td>?</td><td>Any character
 * (<code>Character.isLetter</code>).</td>
 * </tr>
 * <tr><td>*</td><td>Anything.</td></tr>
 * <tr><td>H</td><td>Any hex character (0-9, a-f or A-F).</td></tr>
 * </table>
 *
 * <p>
 * Typically characters correspond to one char, but in certain languages this
 * is not the case. The mask is on a per character basis, and will thus
 * adjust to fit as many chars as are needed.
 * <p>
 * You can further restrict the characters that can be input by the
 * <code>setInvalidCharacters</code> and <code>setValidCharacters</code>
 * methods. <code>setInvalidCharacters</code> allows you to specify
 * which characters are not legal. <code>setValidCharacters</code> allows
 * you to specify which characters are valid. For example, the following
 * code block is equivalent to a mask of '0xHHH' with no invalid/valid
 * characters:
 * <pre>
 * MaskFormatter formatter = new MaskFormatter("0x***");
 * formatter.setValidCharacters("0123456789abcdefABCDEF");
 * </pre>
 * <p>
 * When initially formatting a value if the length of the string is
 * less than the length of the mask, two things can happen. Either
 * the placeholder string will be used, or the placeholder character will
 * be used. Precedence is given to the placeholder string. For example:
 * <pre>
 *   MaskFormatter formatter = new MaskFormatter("###-####");
 *   formatter.setPlaceholderCharacter('_');
 *   formatter.getDisplayValue(tf, "123");
 * </pre>
 * <p>
 * Would result in the string '123-____'. If
 * <code>setPlaceholder("555-1212")</code> was invoked '123-1212' would
 * result. The placeholder String is only used on the initial format,
 * on subsequent formats only the placeholder character will be used.
 * <p>
 * If a <code>MaskFormatter</code> is configured to only allow valid characters
 * (<code>setAllowsInvalid(false)</code>) literal characters will be skipped as
 * necessary when editing. Consider a <code>MaskFormatter</code> with
 * the mask "###-####" and current value "555-1212". Using the right
 * arrow key to navigate through the field will result in (| indicates the
 * position of the caret):
 * <pre>
 *   |555-1212
 *   5|55-1212
 *   55|5-1212
 *   555-|1212
 *   555-1|212
 * </pre>
 * The '-' is a literal (non-editable) character, and is skipped.
 * <p>
 * Similar behavior will result when editing. Consider inserting the string
 * '123-45' and '12345' into the <code>MaskFormatter</code> in the
 * previous example. Both inserts will result in the same String,
 * '123-45__'. When <code>MaskFormatter</code>
 * is processing the insert at character position 3 (the '-'), two things can
 * happen:
 * <ol>
 * <li>If the inserted character is '-', it is accepted.
 * <li>If the inserted character matches the mask for the next non-literal
 * character, it is accepted at the new location.
 * <li>Anything else results in an invalid edit
 * </ol>
 * <p>
 * By default <code>MaskFormatter</code> will not allow invalid edits, you can
 * change this with the <code>setAllowsInvalid</code> method, and will
 * commit edits on valid edits (use the <code>setCommitsOnValidEdit</code> to
 * change this).
 * <p>
 * By default, <code>MaskFormatter</code> is in overwrite mode. That is as
 * characters are typed a new character is not inserted, rather the character
 * at the current location is replaced with the newly typed character. You
 * can change this behavior by way of the method <code>setOverwriteMode</code>.
 * <p>
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases. The current serialization support is
 * appropriate for short term storage or RMI between applications running
 * the same version of Swing.  As of 1.4, support for long term storage
 * of all JavaBeans&trade;
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @since 1.4
 */
public class MaskFormatter extends DefaultFormatter {

  // Potential values in mask.
  private static final char DIGIT_KEY = '#';
  private static final char LITERAL_KEY = '\'';
  private static final char UPPERCASE_KEY = 'U';
  private static final char LOWERCASE_KEY = 'L';
  private static final char ALPHA_NUMERIC_KEY = 'A';
  private static final char CHARACTER_KEY = '?';
  private static final char ANYTHING_KEY = '*';
  private static final char HEX_KEY = 'H';

  private static final MaskCharacter[] EmptyMaskChars = new MaskCharacter[0];

  /**
   * The user specified mask.
   */
  private String mask;

  private transient MaskCharacter[] maskChars;

  /**
   * List of valid characters.
   */
  private String validCharacters;

  /**
   * List of invalid characters.
   */
  private String invalidCharacters;

  /**
   * String used for the passed in value if it does not completely
   * fill the mask.
   */
  private String placeholderString;

  /**
   * String used to represent characters not present.
   */
  private char placeholder;

  /**
   * Indicates if the value contains the literal characters.
   */
  private boolean containsLiteralChars;


  /**
   * Creates a MaskFormatter with no mask.
   */
  public MaskFormatter() {
    setAllowsInvalid(false);
    containsLiteralChars = true;
    maskChars = EmptyMaskChars;
    placeholder = ' ';
  }

  /**
   * Creates a <code>MaskFormatter</code> with the specified mask.
   * A <code>ParseException</code>
   * will be thrown if <code>mask</code> is an invalid mask.
   *
   * @throws ParseException if mask does not contain valid mask characters
   */
  public MaskFormatter(String mask) throws ParseException {
    this();
    setMask(mask);
  }

  /**
   * Sets the mask dictating the legal characters.
   * This will throw a <code>ParseException</code> if <code>mask</code> is
   * not valid.
   *
   * @throws ParseException if mask does not contain valid mask characters
   */
  public void setMask(String mask) throws ParseException {
    this.mask = mask;
    updateInternalMask();
  }

  /**
   * Returns the formatting mask.
   *
   * @return Mask dictating legal character values.
   */
  public String getMask() {
    return mask;
  }

  /**
   * Allows for further restricting of the characters that can be input.
   * Only characters specified in the mask, not in the
   * <code>invalidCharacters</code>, and in
   * <code>validCharacters</code> will be allowed to be input. Passing
   * in null (the default) implies the valid characters are only bound
   * by the mask and the invalid characters.
   *
   * @param validCharacters If non-null, specifies legal characters.
   */
  public void setValidCharacters(String validCharacters) {
    this.validCharacters = validCharacters;
  }

  /**
   * Returns the valid characters that can be input.
   *
   * @return Legal characters
   */
  public String getValidCharacters() {
    return validCharacters;
  }

  /**
   * Allows for further restricting of the characters that can be input.
   * Only characters specified in the mask, not in the
   * <code>invalidCharacters</code>, and in
   * <code>validCharacters</code> will be allowed to be input. Passing
   * in null (the default) implies the valid characters are only bound
   * by the mask and the valid characters.
   *
   * @param invalidCharacters If non-null, specifies illegal characters.
   */
  public void setInvalidCharacters(String invalidCharacters) {
    this.invalidCharacters = invalidCharacters;
  }

  /**
   * Returns the characters that are not valid for input.
   *
   * @return illegal characters.
   */
  public String getInvalidCharacters() {
    return invalidCharacters;
  }

  /**
   * Sets the string to use if the value does not completely fill in
   * the mask. A null value implies the placeholder char should be used.
   *
   * @param placeholder String used when formatting if the value does not completely fill the mask
   */
  public void setPlaceholder(String placeholder) {
    this.placeholderString = placeholder;
  }

  /**
   * Returns the String to use if the value does not completely fill
   * in the mask.
   *
   * @return String used when formatting if the value does not completely fill the mask
   */
  public String getPlaceholder() {
    return placeholderString;
  }

  /**
   * Sets the character to use in place of characters that are not present
   * in the value, ie the user must fill them in. The default value is
   * a space.
   * <p>
   * This is only applicable if the placeholder string has not been
   * specified, or does not completely fill in the mask.
   *
   * @param placeholder Character used when formatting if the value does not completely fill the
   * mask
   */
  public void setPlaceholderCharacter(char placeholder) {
    this.placeholder = placeholder;
  }

  /**
   * Returns the character to use in place of characters that are not present
   * in the value, ie the user must fill them in.
   *
   * @return Character used when formatting if the value does not completely fill the mask
   */
  public char getPlaceholderCharacter() {
    return placeholder;
  }

  /**
   * If true, the returned value and set value will also contain the literal
   * characters in mask.
   * <p>
   * For example, if the mask is <code>'(###) ###-####'</code>, the
   * current value is <code>'(415) 555-1212'</code>, and
   * <code>valueContainsLiteralCharacters</code> is
   * true <code>stringToValue</code> will return
   * <code>'(415) 555-1212'</code>. On the other hand, if
   * <code>valueContainsLiteralCharacters</code> is false,
   * <code>stringToValue</code> will return <code>'4155551212'</code>.
   *
   * @param containsLiteralChars Used to indicate if literal characters in mask should be returned
   * in stringToValue
   */
  public void setValueContainsLiteralCharacters(
      boolean containsLiteralChars) {
    this.containsLiteralChars = containsLiteralChars;
  }

  /**
   * Returns true if <code>stringToValue</code> should return literal
   * characters in the mask.
   *
   * @return True if literal characters in mask should be returned in stringToValue
   */
  public boolean getValueContainsLiteralCharacters() {
    return containsLiteralChars;
  }

  /**
   * Parses the text, returning the appropriate Object representation of
   * the String <code>value</code>. This strips the literal characters as
   * necessary and invokes supers <code>stringToValue</code>, so that if
   * you have specified a value class (<code>setValueClass</code>) an
   * instance of it will be created. This will throw a
   * <code>ParseException</code> if the value does not match the current
   * mask.  Refer to {@link #setValueContainsLiteralCharacters} for details
   * on how literals are treated.
   *
   * @param value String to convert
   * @return Object representation of text
   * @throws ParseException if there is an error in the conversion
   * @see #setValueContainsLiteralCharacters
   */
  public Object stringToValue(String value) throws ParseException {
    return stringToValue(value, true);
  }

  /**
   * Returns a String representation of the Object <code>value</code>
   * based on the mask.  Refer to
   * {@link #setValueContainsLiteralCharacters} for details
   * on how literals are treated.
   *
   * @param value Value to convert
   * @return String representation of value
   * @throws ParseException if there is an error in the conversion
   * @see #setValueContainsLiteralCharacters
   */
  public String valueToString(Object value) throws ParseException {
    String sValue = (value == null) ? "" : value.toString();
    StringBuilder result = new StringBuilder();
    String placeholder = getPlaceholder();
    int[] valueCounter = {0};

    append(result, sValue, valueCounter, placeholder, maskChars);
    return result.toString();
  }

  /**
   * Installs the <code>DefaultFormatter</code> onto a particular
   * <code>JFormattedTextField</code>.
   * This will invoke <code>valueToString</code> to convert the
   * current value from the <code>JFormattedTextField</code> to
   * a String. This will then install the <code>Action</code>s from
   * <code>getActions</code>, the <code>DocumentFilter</code>
   * returned from <code>getDocumentFilter</code> and the
   * <code>NavigationFilter</code> returned from
   * <code>getNavigationFilter</code> onto the
   * <code>JFormattedTextField</code>.
   * <p>
   * Subclasses will typically only need to override this if they
   * wish to install additional listeners on the
   * <code>JFormattedTextField</code>.
   * <p>
   * If there is a <code>ParseException</code> in converting the
   * current value to a String, this will set the text to an empty
   * String, and mark the <code>JFormattedTextField</code> as being
   * in an invalid state.
   * <p>
   * While this is a public method, this is typically only useful
   * for subclassers of <code>JFormattedTextField</code>.
   * <code>JFormattedTextField</code> will invoke this method at
   * the appropriate times when the value changes, or its internal
   * state changes.
   *
   * @param ftf JFormattedTextField to format for, may be null indicating uninstall from current
   * JFormattedTextField.
   */
  public void install(JFormattedTextField ftf) {
    super.install(ftf);
    // valueToString doesn't throw, but stringToValue does, need to
    // update the editValid state appropriately
    if (ftf != null) {
      Object value = ftf.getValue();

      try {
        stringToValue(valueToString(value));
      } catch (ParseException pe) {
        setEditValid(false);
      }
    }
  }

  /**
   * Actual <code>stringToValue</code> implementation.
   * If <code>completeMatch</code> is true, the value must exactly match
   * the mask, on the other hand if <code>completeMatch</code> is false
   * the string must match the mask or the placeholder string.
   */
  private Object stringToValue(String value, boolean completeMatch) throws
      ParseException {
    int errorOffset;

    if ((errorOffset = getInvalidOffset(value, completeMatch)) == -1) {
      if (!getValueContainsLiteralCharacters()) {
        value = stripLiteralChars(value);
      }
      return super.stringToValue(value);
    }
    throw new ParseException("stringToValue passed invalid value",
        errorOffset);
  }

  /**
   * Returns -1 if the passed in string is valid, otherwise the index of
   * the first bogus character is returned.
   */
  private int getInvalidOffset(String string, boolean completeMatch) {
    int iLength = string.length();

    if (iLength != getMaxLength()) {
      // trivially false
      return iLength;
    }
    for (int counter = 0, max = string.length(); counter < max; counter++) {
      char aChar = string.charAt(counter);

      if (!isValidCharacter(counter, aChar) &&
          (completeMatch || !isPlaceholder(counter, aChar))) {
        return counter;
      }
    }
    return -1;
  }

  /**
   * Invokes <code>append</code> on the mask characters in
   * <code>mask</code>.
   */
  private void append(StringBuilder result, String value, int[] index,
      String placeholder, MaskCharacter[] mask)
      throws ParseException {
    for (int counter = 0, maxCounter = mask.length;
        counter < maxCounter; counter++) {
      mask[counter].append(result, value, index, placeholder);
    }
  }

  /**
   * Updates the internal representation of the mask.
   */
  private void updateInternalMask() throws ParseException {
    String mask = getMask();
    ArrayList<MaskCharacter> fixed = new ArrayList<MaskCharacter>();
    ArrayList<MaskCharacter> temp = fixed;

    if (mask != null) {
      for (int counter = 0, maxCounter = mask.length();
          counter < maxCounter; counter++) {
        char maskChar = mask.charAt(counter);

        switch (maskChar) {
          case DIGIT_KEY:
            temp.add(new DigitMaskCharacter());
            break;
          case LITERAL_KEY:
            if (++counter < maxCounter) {
              maskChar = mask.charAt(counter);
              temp.add(new LiteralCharacter(maskChar));
            }
            // else: Could actually throw if else
            break;
          case UPPERCASE_KEY:
            temp.add(new UpperCaseCharacter());
            break;
          case LOWERCASE_KEY:
            temp.add(new LowerCaseCharacter());
            break;
          case ALPHA_NUMERIC_KEY:
            temp.add(new AlphaNumericCharacter());
            break;
          case CHARACTER_KEY:
            temp.add(new CharCharacter());
            break;
          case ANYTHING_KEY:
            temp.add(new MaskCharacter());
            break;
          case HEX_KEY:
            temp.add(new HexCharacter());
            break;
          default:
            temp.add(new LiteralCharacter(maskChar));
            break;
        }
      }
    }
    if (fixed.size() == 0) {
      maskChars = EmptyMaskChars;
    } else {
      maskChars = new MaskCharacter[fixed.size()];
      fixed.toArray(maskChars);
    }
  }

  /**
   * Returns the MaskCharacter at the specified location.
   */
  private MaskCharacter getMaskCharacter(int index) {
    if (index >= maskChars.length) {
      return null;
    }
    return maskChars[index];
  }

  /**
   * Returns true if the placeholder character matches aChar.
   */
  private boolean isPlaceholder(int index, char aChar) {
    return (getPlaceholderCharacter() == aChar);
  }

  /**
   * Returns true if the passed in character matches the mask at the
   * specified location.
   */
  private boolean isValidCharacter(int index, char aChar) {
    return getMaskCharacter(index).isValidCharacter(aChar);
  }

  /**
   * Returns true if the character at the specified location is a literal,
   * that is it can not be edited.
   */
  private boolean isLiteral(int index) {
    return getMaskCharacter(index).isLiteral();
  }

  /**
   * Returns the maximum length the text can be.
   */
  private int getMaxLength() {
    return maskChars.length;
  }

  /**
   * Returns the literal character at the specified location.
   */
  private char getLiteral(int index) {
    return getMaskCharacter(index).getChar((char) 0);
  }

  /**
   * Returns the character to insert at the specified location based on
   * the passed in character.  This provides a way to map certain sets
   * of characters to alternative values (lowercase to
   * uppercase...).
   */
  private char getCharacter(int index, char aChar) {
    return getMaskCharacter(index).getChar(aChar);
  }

  /**
   * Removes the literal characters from the passed in string.
   */
  private String stripLiteralChars(String string) {
    StringBuilder sb = null;
    int last = 0;

    for (int counter = 0, max = string.length(); counter < max; counter++) {
      if (isLiteral(counter)) {
        if (sb == null) {
          sb = new StringBuilder();
          if (counter > 0) {
            sb.append(string.substring(0, counter));
          }
          last = counter + 1;
        } else if (last != counter) {
          sb.append(string.substring(last, counter));
        }
        last = counter + 1;
      }
    }
    if (sb == null) {
      // Assume the mask isn't all literals.
      return string;
    } else if (last != string.length()) {
      if (sb == null) {
        return string.substring(last);
      }
      sb.append(string.substring(last));
    }
    return sb.toString();
  }


  /**
   * Subclassed to update the internal representation of the mask after
   * the default read operation has completed.
   */
  private void readObject(ObjectInputStream s)
      throws IOException, ClassNotFoundException {
    s.defaultReadObject();
    try {
      updateInternalMask();
    } catch (ParseException pe) {
      // assert();
    }
  }

  /**
   * Returns true if the MaskFormatter allows invalid, or
   * the offset is less than the max length and the character at
   * <code>offset</code> is a literal.
   */
  boolean isNavigatable(int offset) {
    if (!getAllowsInvalid()) {
      return (offset < getMaxLength() && !isLiteral(offset));
    }
    return true;
  }

  /*
   * Returns true if the operation described by <code>rh</code> will
   * result in a legal edit.  This may set the <code>value</code>
   * field of <code>rh</code>.
   * <p>
   * This is overriden to return true for a partial match.
   */
  boolean isValidEdit(ReplaceHolder rh) {
    if (!getAllowsInvalid()) {
      String newString = getReplaceString(rh.offset, rh.length, rh.text);

      try {
        rh.value = stringToValue(newString, false);

        return true;
      } catch (ParseException pe) {
        return false;
      }
    }
    return true;
  }

  /**
   * This method does the following (assuming !getAllowsInvalid()):
   * iterate over the max of the deleted region or the text length, for
   * each character:
   * <ol>
   * <li>If it is valid (matches the mask at the particular position, or
   * matches the literal character at the position), allow it
   * <li>Else if the position identifies a literal character, add it. This
   * allows for the user to paste in text that may/may not contain
   * the literals.  For example, in pasing in 5551212 into ###-####
   * when the 1 is evaluated it is illegal (by the first test), but there
   * is a literal at this position (-), so it is used.  NOTE: This has
   * a problem that you can't tell (without looking ahead) if you should
   * eat literals in the text. For example, if you paste '555' into
   * #5##, should it result in '5555' or '555 '? The current code will
   * result in the latter, which feels a little better as selecting
   * text than pasting will always result in the same thing.
   * <li>Else if at the end of the inserted text, the replace the item with
   * the placeholder
   * <li>Otherwise the insert is bogus and false is returned.
   * </ol>
   */
  boolean canReplace(ReplaceHolder rh) {
    // This method is rather long, but much of the burden is in
    // maintaining a String and swapping to a StringBuilder only if
    // absolutely necessary.
    if (!getAllowsInvalid()) {
      StringBuilder replace = null;
      String text = rh.text;
      int tl = (text != null) ? text.length() : 0;

      if (tl == 0 && rh.length == 1 && getFormattedTextField().
          getSelectionStart() != rh.offset) {
        // Backspace, adjust to actually delete next non-literal.
        while (rh.offset > 0 && isLiteral(rh.offset)) {
          rh.offset--;
        }
      }
      int max = Math.min(getMaxLength() - rh.offset,
          Math.max(tl, rh.length));
      for (int counter = 0, textIndex = 0; counter < max; counter++) {
        if (textIndex < tl && isValidCharacter(rh.offset + counter,
            text.charAt(textIndex))) {
          char aChar = text.charAt(textIndex);
          if (aChar != getCharacter(rh.offset + counter, aChar)) {
            if (replace == null) {
              replace = new StringBuilder();
              if (textIndex > 0) {
                replace.append(text.substring(0, textIndex));
              }
            }
          }
          if (replace != null) {
            replace.append(getCharacter(rh.offset + counter,
                aChar));
          }
          textIndex++;
        } else if (isLiteral(rh.offset + counter)) {
          if (replace != null) {
            replace.append(getLiteral(rh.offset + counter));
            if (textIndex < tl) {
              max = Math.min(max + 1, getMaxLength() -
                  rh.offset);
            }
          } else if (textIndex > 0) {
            replace = new StringBuilder(max);
            replace.append(text.substring(0, textIndex));
            replace.append(getLiteral(rh.offset + counter));
            if (textIndex < tl) {
              // Evaluate the character in text again.
              max = Math.min(max + 1, getMaxLength() -
                  rh.offset);
            } else if (rh.cursorPosition == -1) {
              rh.cursorPosition = rh.offset + counter;
            }
          } else {
            rh.offset++;
            rh.length--;
            counter--;
            max--;
          }
        } else if (textIndex >= tl) {
          // placeholder
          if (replace == null) {
            replace = new StringBuilder();
            if (text != null) {
              replace.append(text);
            }
          }
          replace.append(getPlaceholderCharacter());
          if (tl > 0 && rh.cursorPosition == -1) {
            rh.cursorPosition = rh.offset + counter;
          }
        } else {
          // Bogus character.
          return false;
        }
      }
      if (replace != null) {
        rh.text = replace.toString();
      } else if (text != null && rh.offset + tl > getMaxLength()) {
        rh.text = text.substring(0, getMaxLength() - rh.offset);
      }
      if (getOverwriteMode() && rh.text != null) {
        rh.length = rh.text.length();
      }
    }
    return super.canReplace(rh);
  }


  //
  // Interal classes used to represent the mask.
  //
  private class MaskCharacter {

    /**
     * Subclasses should override this returning true if the instance
     * represents a literal character. The default implementation
     * returns false.
     */
    public boolean isLiteral() {
      return false;
    }

    /**
     * Returns true if <code>aChar</code> is a valid reprensentation of
     * the receiver. The default implementation returns true if the
     * receiver represents a literal character and <code>getChar</code>
     * == aChar. Otherwise, this will return true is <code>aChar</code>
     * is contained in the valid characters and not contained
     * in the invalid characters.
     */
    public boolean isValidCharacter(char aChar) {
      if (isLiteral()) {
        return (getChar(aChar) == aChar);
      }

      aChar = getChar(aChar);

      String filter = getValidCharacters();

      if (filter != null && filter.indexOf(aChar) == -1) {
        return false;
      }
      filter = getInvalidCharacters();
      if (filter != null && filter.indexOf(aChar) != -1) {
        return false;
      }
      return true;
    }

    /**
     * Returns the character to insert for <code>aChar</code>. The
     * default implementation returns <code>aChar</code>. Subclasses
     * that wish to do some sort of mapping, perhaps lower case to upper
     * case should override this and do the necessary mapping.
     */
    public char getChar(char aChar) {
      return aChar;
    }

    /**
     * Appends the necessary character in <code>formatting</code> at
     * <code>index</code> to <code>buff</code>.
     */
    public void append(StringBuilder buff, String formatting, int[] index,
        String placeholder)
        throws ParseException {
      boolean inString = index[0] < formatting.length();
      char aChar = inString ? formatting.charAt(index[0]) : 0;

      if (isLiteral()) {
        buff.append(getChar(aChar));
        if (getValueContainsLiteralCharacters()) {
          if (inString && aChar != getChar(aChar)) {
            throw new ParseException("Invalid character: " +
                aChar, index[0]);
          }
          index[0] = index[0] + 1;
        }
      } else if (index[0] >= formatting.length()) {
        if (placeholder != null && index[0] < placeholder.length()) {
          buff.append(placeholder.charAt(index[0]));
        } else {
          buff.append(getPlaceholderCharacter());
        }
        index[0] = index[0] + 1;
      } else if (isValidCharacter(aChar)) {
        buff.append(getChar(aChar));
        index[0] = index[0] + 1;
      } else {
        throw new ParseException("Invalid character: " + aChar,
            index[0]);
      }
    }
  }


  /**
   * Used to represent a fixed character in the mask.
   */
  private class LiteralCharacter extends MaskCharacter {

    private char fixedChar;

    public LiteralCharacter(char fixedChar) {
      this.fixedChar = fixedChar;
    }

    public boolean isLiteral() {
      return true;
    }

    public char getChar(char aChar) {
      return fixedChar;
    }
  }


  /**
   * Represents a number, uses <code>Character.isDigit</code>.
   */
  private class DigitMaskCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return (Character.isDigit(aChar) &&
          super.isValidCharacter(aChar));
    }
  }


  /**
   * Represents a character, lower case letters are mapped to upper case
   * using <code>Character.toUpperCase</code>.
   */
  private class UpperCaseCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return (Character.isLetter(aChar) &&
          super.isValidCharacter(aChar));
    }

    public char getChar(char aChar) {
      return Character.toUpperCase(aChar);
    }
  }


  /**
   * Represents a character, upper case letters are mapped to lower case
   * using <code>Character.toLowerCase</code>.
   */
  private class LowerCaseCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return (Character.isLetter(aChar) &&
          super.isValidCharacter(aChar));
    }

    public char getChar(char aChar) {
      return Character.toLowerCase(aChar);
    }
  }


  /**
   * Represents either a character or digit, uses
   * <code>Character.isLetterOrDigit</code>.
   */
  private class AlphaNumericCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return (Character.isLetterOrDigit(aChar) &&
          super.isValidCharacter(aChar));
    }
  }


  /**
   * Represents a letter, uses <code>Character.isLetter</code>.
   */
  private class CharCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return (Character.isLetter(aChar) &&
          super.isValidCharacter(aChar));
    }
  }


  /**
   * Represents a hex character, 0-9a-fA-F. a-f is mapped to A-F
   */
  private class HexCharacter extends MaskCharacter {

    public boolean isValidCharacter(char aChar) {
      return ((aChar == '0' || aChar == '1' ||
          aChar == '2' || aChar == '3' ||
          aChar == '4' || aChar == '5' ||
          aChar == '6' || aChar == '7' ||
          aChar == '8' || aChar == '9' ||
          aChar == 'a' || aChar == 'A' ||
          aChar == 'b' || aChar == 'B' ||
          aChar == 'c' || aChar == 'C' ||
          aChar == 'd' || aChar == 'D' ||
          aChar == 'e' || aChar == 'E' ||
          aChar == 'f' || aChar == 'F') &&
          super.isValidCharacter(aChar));
    }

    public char getChar(char aChar) {
      if (Character.isDigit(aChar)) {
        return aChar;
      }
      return Character.toUpperCase(aChar);
    }
  }
}
